It is well known in the prior art that raw peanuts must be roasted in order to make peanut butter. The most common prior-art method of making peanut butter is schematically depicted in FIG. 1. Shelled raw peanuts are roasted by the application of external heat. The roasted peanuts are then ground to a consistency known as peanut butter.
The product resulting from this prior-art method suffers from several disadvantages. A first disadvantage results from the fact that peanuts are a poor conductor of heat. When peanuts are roasted prior to grinding, the periphery tends to become over-roasted and the center under-roasted, resulting in uneven roast flavors. A second disadvantage is that peanut butter produced in this manner will not "keep" as long. During grinding, peanut oil separates from peanut solids. Over time, the separated oil will oxidize, causing the peanut butter to have a rancid taste or odor. Another disadvantage is that the heat generated during comminution of the roasted peanuts is generally considered to be deleterious to flavor production. Yet another disadvantage is the pollution and loss of flavor that results from roasting whole raw peanuts by the application of external heat such as hot air furnaces. When peanuts are roasted in this way, a substantial amount of the peanut flavor escapes from roasting facilities, not only resulting in unnecessary peanut flavor loss, but also causing a potentially offensive odor to the surrounding community.
Applicant's U.S. Pat. No. 3,121,015 discloses a process for making peanut butter which solves some of the problems associated with roasting prior to grinding. This method is schematically depicted in FIG. 2. Shelled raw peanuts are ground to a slurry of comminuted peanut particles and peanut oil. Although some heat is generated during grinding, the heat is insufficient to raise the temperature of the slurry to a roasting temperature. Therefore, external heat is applied in the form of, for example, a stirring kettle or dielectric heaters to raise the temperature of the slurry to a roasting temperature. Once a sufficient amount of time has passed to develop the desired roast flavor, the slurry is rapidly cooled by for example introducing a refrigerated coolant into the stirring kettle jacket.
While applicant's prior art process overcomes some of the problems associated with roasting prior to grinding, it also suffers from certain disadvantages. Most notably, it is difficult to evenly heat the slurry with external heat. This is particularly true when trying to produce large quantities of peanut butter in a commercially practicable process. Even when the slurry is stirred, the outer portions tend to become over-roasted and the center portions under-roasted, resulting in uneven roast flavors. Therefore, in order to obtain the advantages of roasting after grinding using this method, it is necessary to make smaller batches, and numerous external heat apparatuses for roasting are required to produce substantial quantities. There would thus be substantial cost savings if the roasting could be accomplished in a commercially practicable way that does not require numerous external heat apparatuses. Another problem associated with roasting with external heat is the tendency for particle solids to stick to the heating surface as a result of proteins being charred by overheating.
The same shortcomings exist in the prior art methods of making nut butters other than peanut butter. Examples include almond butter and cashew butter. Similar disadvantages are also found in the prior art methods of roasting other food slurries which contain nuts, as for example beverage flavor bases.
It is also well known in the prior art that coffee beans must be roasted before being made into coffee. However, the prior art method of roasting whole coffee beans with external heat suffers from similar disadvantages as that of roasting peanuts. These disadvantages primarily include the development of uneven roast flavors and the flavor loss and pollution which result from roasting with external heat.
What has been needed is a peanut butter and a simple process for making peanut butter which overcome the problems associated with roasting prior to grinding, including uneven roast flavors and premature oxidation, and which is commercially practicable. What has also been needed is a process for roasting food slurries, such as those containing nuts and coffee beans, which overcomes the problems associated with prior art methods.